Vacuum flask with tin phosphorus oxide sealing glass

ABSTRACT

Metal-walled vacuum flasks including tin phosphorus oxide sealing glass, and methods of sealing an exhaust aperture for a metal-walled vacuum flask, including disposing a tin phosphorus oxide sealing glass frit adjacent the exhaust aperture, applying a vacuum to the metal-walled vacuum flask; and raising a temperature of the sealing glass frit under the vacuum sufficiently that the sealing glass flows and seals the exhaust aperture.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the priority under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 62/045,964, filed Sep. 4, 2014, the disclosure of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a metal-walled vacuum flasks, and in particular to metal-walled vacuum flasks having an exhaust opening sealed using a lead-free sealing glass.

BACKGROUND

A vacuum flask, or vacuum-insulated flask, is an insulated storage vessel consisting of two flasks, placed one within the other and joined at the neck. The space between the two flasks is at least partially evacuated, and the resulting near-vacuum substantially prevents heat transfer to or from the contents of the flask by either conduction or convection. The contents of a vacuum flask may therefore remain either hotter or cooler than the flask's environment for an extended period of time. A variety of vacuum flasks are sold commercially as beverage containers, and are designed to keep beverages either hot or cold for long periods.

During vacuum flask manufacture, after the inner and outer flasks are joined together and sealed, and a small exhaust aperture is left in the outer flask so that the internal space between the inner and outer flasks may be evacuated. The exhaust aperture must be sealed while the flask is under vacuum, and typically the aperture is sealed using sealing glass. That is, a portion of sealing glass is placed on or adjacent the exhaust aperture, and the vacuum flask is placed into a vacuum furnace. Heating the vacuum flask under vacuum results in the evacuation of the internal space between the inner and outer flasks, and the sealing glass softening and deforming so as to cover and seal the exhaust aperture.

Previously, lead-containing sealing glass has been used to seal vacuum flasks in this way. However, the use of lead-containing materials in manufacturing represents a potential health risk to manufacturers, as well as to the end user of the flask. Local environmental regulations may also limit the sale of lead-containing products in some areas.

SUMMARY

The present disclosure provides metal-walled vacuum flasks, and methods of sealing exhaust apertures for metal-walled vacuum flasks.

In some aspects, the present disclosure provides methods of sealing an exhaust aperture for a metal-walled flask, including disposing a tin phosphorus oxide sealing glass frit adjacent the exhaust aperture, applying a vacuum to the metal-walled flask, and raising the temperature of the sealing glass frit under the vacuum sufficiently that the sealing glass flows and seals the exhaust aperture.

In another aspect, the present disclosure provides a metal-walled vacuum flask, including a metal inner bottle and a metal outer bottle, where the neck portion of the inner bottle is connected to the neck portion of the outer bottle to form an enclosed space between the inner bottle and the outer bottle that is substantially evacuated, and where the aperture in the outer bottle used to evacuate the enclosed space is sealed by a tin phosphorus oxide sealing glass.

In another aspect, the present disclosure provides a metal-walled vacuum flask having an inner bottle and an outer bottle, where the vacuum flask is prepared by disposing a tin phosphorus oxide sealing glass frit adjacent to an exhaust aperture in the outer bottle, applying a vacuum to the metal-walled flask, and raising a temperature of the sealing glass frit under a vacuum sufficiently that the sealing glass flows and seals the exhaust aperture.

Various features, functions, and advantages of the present disclosure may be achieved independently in various embodiments of the disclosure, or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a perspective view of an exemplary metal-walled vacuum flask that is oriented neck downwards, according to an embodiment of the present disclosure.

FIG. 2 depicts a side elevation view of the metal-walled vacuum flask of FIG. 1.

FIG. 3 depicts a cross-section view of the metal-walled vacuum flask of FIGS. 1 and 2 as indicated in FIG. 2.

FIG. 4 depicts an enlarged view of the base of the metal-walled vacuum flask before sealing, as indicated in FIG. 3.

FIG. 5 depicts the base of the metal-walled vacuum flask of FIG. 4, after sealing.

FIG. 6 depicts a schematic view of an illustrative vacuum furnace useful for sealing the metal-walled vacuum flasks of the present disclosure.

FIG. 7 is a plot showing an ideal temperature profile for a vacuum furnace according to the illustrated method, and an experimental temperature profile for a vacuum furnace according to the illustrated method.

FIG. 8 is a flowchart illustrating a method of sealing an exhaust aperture for a metal-walled vacuum flask, according to the present disclosure.

DETAILED DESCRIPTION

FIG. 1 depicts an illustrative metal-walled vacuum flask 10 according to the present invention prior to evacuation and sealing. The vacuum flask 10 is shown with the bottom or underside 12 of the flask upward, and the neck portion 14 of the vacuum flask directed downward. FIG. 2 depicts the vacuum flask 10 in a side view, and FIG. 3 depicts a cross-section view of flask 10, along the line indicated in FIG. 2.

As shown in the cross-section view of FIG. 3, flask 10 includes an outer bottle 16 and an inner bottle 18, where the outer bottle 16 and inner bottle 18 are connected at the neck portion 14 of the flask. The internal volume 20 of the vacuum flask 10 is defined and enclosed by the inner bottle 18. The space 22 that exists between the walls of the outer bottle 16 and the inner bottle 18 will be evacuated to provide thermal insulation for the vacuum flask 10. A portion of the cross-section of FIG. 3 is shown in greater detail in FIG. 4, including outer bottle 16, inner bottle 18, and the enclosed spaces 20 and 22, respectively.

To facilitate the evacuation of the internal wall space 22, an exhaust aperture 24 is formed in outer bottle 16 on the underside 12 of the vacuum flask 10, as shown in FIG. 4. In one aspect of the present disclosure, the internal wall space 22 may be evacuated, and then exhaust aperture 24 may be sealed to preserve the internal vacuum.

In one aspect of the disclosure, the use of a sealing glass to seal aperture 24 may be advantageous. The term “sealing glass” may refer to any of a wide variety of glass compositions (amorphous solids) that may be used to form seals to/with metal surfaces. The sealing glass may be a substantially lead-free composition of sealing glass. In particular, the sealing glass may be a tin phosphorus oxide sealing glass. That is, the glass composition may include tin oxides and phosphorus oxides. The glass composition may include one or more additional components in order to adjust one or more characteristics of the sealing glass, such as melting point, coefficient of thermal expansion, and the like, provided that the composition is substantially lead-free.

More particularly, the tin phosphorus oxide sealing glass of the present disclosure may have the formula SnO.P₂O₅. A particularly useful formulation of sealing glass for sealing the vacuum flasks of the present disclosure may be obtained from Asahi Glass Company (AGC), under catalog no. 9079-150.

The tin phosphorus oxide sealing glass of the present disclosure may be used in the form of a powder glass, a glass paste, or a preformed powder glass frit. Powder glass frits may be formed by fusing powdered glass in a fusing oven. It should be appreciated that any configuration of preformed glass frit that is suitable for sealing the exhaust aperture 24 is a suitable configuration for the purposes of this disclosure. Typically, the glass frit may be formed into a pellet, such as a spherical pellet, hemispherical pellet, oblong pellet, cubic pellet, or lozenge-shaped pellet, among many others.

The sealing glass of the present disclosure may be used to seal exhaust aperture 24 by disposing an appropriate sealing glass pellet in a location and/or with an appropriate orientation such that when the sealing glass pellet is heated it will soften and flow to cover the exhaust aperture.

Generally speaking, a selected formulation of sealing glass will soften and flow when the temperature of the glass is raised above the glass transition temperature for that formulation. The glass transition temperature (or T_(g)) is the temperature at which an amorphous material transitions from a hard and relatively brittle state into a molten or at least semi-fluid state. It should be appreciated that for many glass compositions the glass transition temperature is not a specific temperature reflecting a sharp phase transition, but is more properly a phenomenon observed over a range of temperatures bounded by the glass transition starting temperature (T_(s)) and the glass transition finishing temperature (T_(f)).

In one aspect of the present disclosure, the vacuum flask 10 is inverted, and the sealing glass 26 is disposed on and above a depression 28 in the surface of outer bottle 16, as shown in FIG. 4. In this embodiment the exhaust aperture 24 is disposed at a low point in the depression 28, and so as the sealing glass pellet 26 is heated above its T_(g) or T_(s) and softens and flows it will cover the exhaust aperture 24, and upon cooling the sealing glass 29 may form an airtight seal as shown in FIG. 6. However, the sealing glass pellet 26 may be disposed on the vacuum flask in any location and with any orientation that may facilitate the sealing of an exhaust aperture 24 when the sealing glass pellet is softened by heating and reflows.

Although enclosed space 22 may be satisfactorily evacuated mechanically, for example by a vacuum pump, it may be additionally advantageous to remove any residual or leftover gases such as H₂, CO₂, CO, N₂, and H₂O, among others, from the enclosed space 22 after the exhaust aperture 24 is sealed. The enclosed space 22 may therefore optionally further include a getter material 30 configured to complete and/or maintain the vacuum within enclosed space 22. Getter material 30 may be mechanically retained in place, for example by a clip or partial enclosure 32, provided that the partial enclosure 32 provides access for gas molecules to reach the getter material 30. A getter material 30 may be configured to react chemically with gas molecules, or may be configured to adsorb gas molecules, but in either case the getter material removes most or all of the remaining gas molecules from the enclosed space 22 after the exhaust aperture 24 is sealed.

A variety of getter materials 30 may be used within enclosed space 22, but the getter material 30 is typically selected to remain inactive until after enclosed space 22 is substantially evacuated, and may require an activation process in order to become active and scavenge residual gas molecules from the enclosed space 22. In one aspect of the present disclosure, the getter material 30 is present as a getter pellet that may be activated by heating under vacuum. For example, getter material 30 may be selected to be activated by heating to a temperature of 450° C. for at least about 10 minutes, although this activation time may be reduced if higher temperatures are used, or alternative getter materials are selected that have a lower activation threshold.

In one aspect of the present disclosure, the vacuum flask 10 may be evacuated and heated simultaneously, for example using a vacuum furnace 34. Vacuum furnace 34 may be configured to be capable of heating a sealing glass pellet 26 to a temperature sufficient for it to soften, reflow, and seal the exhaust aperture 24 while the vacuum flask 10 is subjected to an applied vacuum. Any vacuum furnace 34 that can at least substantially evacuate the vacuum flask interior space while heating the vacuum flask is an acceptable vacuum furnace for the purposes of this disclosure. The vacuum furnace may employ any suitable heating means, such as electric (resistive) heating elements to bake the vacuum flask 10, activate the getter material 30, and reflow the sealing glass pellet 26 to seal the exhaust aperture 24.

For the purposes of economy, the vacuum furnace 34 may be configured to evacuate and heat multiple individual vacuum flasks 10 simultaneously, as shown in FIG. 6. For example, selected vacuum furnaces may accommodate a furnace rack that may be loaded with approximately 1000 vacuum flasks, each preloaded with its own sealing glass pellet.

A more robust hermetic seal may be achieved using the selected sealing glass where the temperature profile of the vacuum furnace 34 may be accurately controlled. The temperature profile may be selected based upon both the composition of the sealing glass used, the size of the sealing glass pellet selected, and the relationship between the furnace temperature set point and the actual temperature of the vacuum flask and/or sealing glass pellet. For example, where a selected sealing glass formulation and/or morphology may exhibit higher than typical infrared reflectance, the rate of heating of the sealing glass may be reduced, and longer heating times may therefore be required to achieve an equivalent result. Alternatively or in addition, the configuration of the vacuum furnace, including the internal geometry, arrangement of heating elements, and configuration of vacuum flasks, may affect the efficiency of heat transfer and therefore the temperature profile may vary. One of skill in the art would be fully capable of optimizing such parameters as temperature set point and duration of heating needed to achieve the desired result, whether it is to emphasize speed and throughput, or to maximize energy efficiency.

For the purposes of the present disclosure, and with respect to a representative tin phosphorus oxide sealing glass formulation, the vacuum furnace may initially be preheated to approximately 250° C. Upon loading the furnace with nonsealed vacuum flasks already equipped with sealing glass pellets and optionally a selected getter material, the furnace may be sealed and evacuated. The furnace temperature may then be increased to a temperature of approximately 600° C. This increase in temperature may take from approximately 100 to approximately 120 minutes. The temperature of the vacuum furnace may then be held at approximately 600° C. for a period of time of about 60 minutes, at which point the vacuum furnace may be allowed to slowly cool, for example taking at least 160 minutes to reach a temperature of about 270° C.

The applied vacuum should not be broken until the furnace temperature drops below about 270° C., as releasing the vacuum before the glass seal has completely solidified may result in failure of the glass seal. Releasing the vacuum while the glass seal remains semi-solid may result in still-pliable glass being pushed through the exhaust aperture and into the internal space of the vacuum flask, or the semi-viscous seal may simply crack and fail when exposed to the pressure difference.

An exemplary temperature profile that may be suitable for the purposes of the present disclosure is provided in FIG. 7. In the plot of FIG. 7, the curve marked by solid circles and solid lines represents an ideal temperature profile, while the curve marked by open squares and dashed lines represents a trial temperature profile conducted using vacuum flasks in combination with a tin phosphorus oxide sealing glass according to the present disclosure.

FIG. 8 includes a flowchart 40 depicted an illustrative method of sealing an exhaust aperture for a metal-walled vacuum flask, including disposing a tin phosphorus oxide sealing glass frit adjacent the exhaust aperture at 42 of flowchart 40; applying a vacuum to the metal-walled vacuum flask at 44 of flowchart 40; and raising the temperature of the sealing glass frit under the vacuum sufficiently that the sealing glass flows and seals the exhaust aperture at 46 of flowchart 40.

The use of a tin phosphorus oxide sealing glass results in the elimination of any lead from the finished product that may have otherwise been introduced by a lead-containing frit seal material. The resulting product may be certified as a lead-free product and be marketed for sale within more markets.

In addition, the temperature profile used for sealing the vacuum flasks using the tin phosphorus oxide glass frit may be substantially lower than the temperatures required for alternative lead-free sealing glass formulations, such as those based upon bismuth oxide glasses, which may require temperatures higher than those needed for lead-based sealing glasses. By reducing the temperature required to form a robust and stable seal, the overall processing time for the vacuum flasks may be reduced, even when maintaining the same rate of heating or rate of cooling. Furthermore, lower peak vacuum furnace temperatures correlate with reduced energy costs per batch of vacuum flasks produced.

Although the present invention has been shown and described with reference to the foregoing operational principles and preferred embodiments, it will be apparent to those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the appended claims. The present invention is intended to embrace all such alternatives, modifications and variances that fall within the scope of the claims.

The disclosure set forth above may encompass multiple distinct inventions with independent utility. While each of these inventions has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the inventions include all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. Similarly, where the claims recite “a” or “a first” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.

Inventions embodied in various combinations and subcombinations of features, functions, elements, and/or properties may be claimed through presentation of new claims in a related application. Such new claims, whether they are directed to a different invention or directed to the same invention, whether different, broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of the inventions of the present disclosure. 

What is claimed is:
 1. A method of sealing an exhaust aperture for a metal-walled vacuum flask, comprising: disposing a sealing glass frit adjacent the exhaust aperture, wherein the sealing glass is a tin phosphorus oxide glass; applying a vacuum to the metal-walled vacuum flask; and raising a temperature of the sealing glass frit under the vacuum sufficiently that the sealing glass flows and seals the exhaust aperture.
 2. The method of claim 1, wherein disposing the tin phosphorus oxide sealing glass frit includes disposing a sealing glass frit including glass having the formula SnO.P₂O₅.
 3. The method of claim 1, wherein disposing the sealing glass frit includes disposing a sealing glass frit that is substantially lead-free.
 4. The method of claim 1, further comprising loading the metal-walled vacuum flask into a vacuum furnace for heating.
 5. The method of claim 4, further comprising preheating the vacuum furnace prior to loading the metal-walled vacuum flask into the vacuum furnace.
 6. The method of claim 4, further comprising preheating the vacuum furnace to at least about 250° C. prior to loading the metal-walled vacuum flask into the vacuum furnace.
 7. The method of claim 1, wherein raising the temperature of the sealing glass frit includes heating the sealing glass frit to a temperature above the glass transition temperature (T_(g)) of the sealing glass frit.
 8. The method of claim 7, further comprising holding the sealing glass at a temperature above the glass transition temperature of the sealing glass for at least about 100 minutes.
 9. The method of claim 7, wherein raising the temperature of the sealing glass frit includes heating the vacuum furnace to approximately 600° C.
 10. The method of claim 9, further comprising holding the vacuum furnace at approximately 600° C. for approximately 100 to approximately 120 minutes.
 11. The method of claim 9, further comprising cooling the vacuum furnace to approximately 270° C.
 12. A metal-walled vacuum flask, comprising a metal inner bottle and a metal outer bottle; wherein a neck portion of the inner bottle is connected to a neck portion of the outer bottle to form an enclosed space between the inner bottle and said outer bottle; wherein the enclosed space is substantially evacuated; and wherein an aperture in the outer bottle used to evacuate the enclosed space is sealed by a tin phosphorus oxide sealing glass.
 13. A metal-walled vacuum flask having an inner bottle and an outer bottle, prepared by a method comprising: disposing a sealing glass frit adjacent an exhaust aperture in the outer bottle, wherein the sealing glass is a tin phosphorus oxide glass; applying a vacuum to the metal-walled flask; and raising a temperature of the sealing glass frit under a vacuum sufficiently that the sealing glass flows and seals the exhaust aperture.
 14. The metal-walled vacuum flask of claim 13, wherein disposing the tin phosphorus oxide sealing glass frit includes disposing a sealing glass frit wherein the glass has the formula SnO.P₂O₅.
 15. The metal-walled vacuum flask of claim 10, wherein the vacuum is applied to the metal-walled flask and the temperature of the sealing glass frit is raised above the glass transition temperature (T_(g)) of the sealing glass frit while the metal-walled flask is disposed in a vacuum furnace. 